Making tiny indentations in the shells of windowpane oysters (Placuna placenta) has revealed how the protective layer keeps from crumbling, even after multiple hits. The shells are made of layered, diamond-shaped calcite crystals. When stressed, the atoms of the crystals at the impact point move a short distance, mirroring the pattern of the original crystal structure.

The process spurs other changes, such as stretching of material between crystals, that confine the damage to a small area, res...